In a typical inkjet recording or printing system, ink droplets are ejected from a nozzle at high speed towards a recording element or medium to produce an image on the medium. The ink droplets, or recording liquid, generally comprise a recording agent, such as a dye or pigment, and a large amount of solvent. The solvent, or carrier liquid, typically is made up of water, an organic material such as a monohydric alcohol, a polyhydric alcohol or mixtures thereof.
An inkjet recording element typically comprises a support having on at least one surface thereof at least one ink-receiving layer. The ink-receiving layer is typically either a porous layer that imbibes the ink via capillary action or a polymer layer that swells to absorb the ink. Transparent swellable hydrophilic polymer layers do not scatter light and therefore afford optimal image density and gamut, but may take an undesirably long time to dry. Porous ink-receiving layers are usually composed of inorganic or organic particles bonded together by a binder. During the inkjet printing process, ink droplets are rapidly absorbed into the coating through capillary action, and the image is dry-to-touch right after it comes out of the printer. Therefore, porous coatings allow a fast “drying” of the ink and produce a smear-resistant image; however, porous layers, by virtue of the large number of air-particle interfaces, scatter light that may result in lower densities of printed images.
Furthermore, inkjet prints prepared by printing onto inkjet recording elements are subject to environmental degradation. They are especially vulnerable to damage resulting from contact with water and atmospheric gases such as ozone. Ozone can bleach inkjet dyes resulting in loss of density. Porous layers are particularly vulnerable to atmospheric gases in view of the open pores. The damage resulting from the post-imaging contact with water can take the form of water spots resulting from deglossing of the top coat, dye smearing due to unwanted dye diffusion, and even gross dissolution of the image recording layer. To overcome these deficiencies, inkjet prints are often laminated. However, lamination is expensive, requiring a separate roll of material.
Efforts have been made to avoid lamination and yet provide protected inkjet prints by providing an inkjet receiver having an uppermost fusible, porous layer. Such inkjet elements are known in the art. Fusing the upper layer after printing the image has the advantage of both providing a protective overcoat for water and stain resistance and reducing light scatter for improved image quality.
For example, U.S. Pat. Nos. 4,785,313 and 4,832,984 relate to an inkjet recording element comprising a support having thereon an upper fusible, porous ink-transporting layer and a lower swellable polymeric ink-retaining layer, wherein the ink-retaining layer is non-porous.
EP 858905A1 relates to an inkjet recording element having a fusible porous ink-transporting outermost layer, formed by heat sintering thermoplastic particles, and an underlying porous ink-retaining layer to absorb and retain the ink applied to the outermost layer to form an image. The underlying porous ink-retaining layer is constituted mainly of refractory pigments. After imaging, the outermost layer is made non-porous.
EP 1,188,573 A2 relates to an inkjet recording material comprising in order: a sheet-like paper substrate, at least one pigment layer coated thereon, and at least one sealing layer coated thereon. Also disclosed is an optional dye-trapping layer present between the pigment layer and the sealing layer.
U.S. Pat. No. 6,497,480 to Wexler discloses inkjet media comprising both a fusible ink-transporting layer and a fusible dye-trapping layer. A base layer under the fusible layers may be employed to absorb ink-carrier-liquid fluid.
Protective overcoats and crosslinked overcoats for imaging elements are also known in the art. For example, U.S. Pat. No. 6,436,617 relates to protective overcoats, for photographic image elements, comprising water-dispersible latex particles, which particles comprise an epoxy material and a thermoplastic acid polymer, a water-soluble hydrophilic polymer, and a hydrophobically modified associative thickener. The hydrophilic polymer is substantially washed out during photographic processing facilitating the coalescence of the other materials. Another driving force for this coalescence is the elevated temperature during the drying associated with photoprocessing.
U.S. Pat. No. 6,548,182 relates to an inkjet recording material wherein a coating comprises a water-soluble polymer having a plurality of carboxyl groups in combination with a water-soluble oxazoline compound as a crosslinking agent. EP 0 320 594 A2 discloses aqueous crosslinkable resin dispersions for use in fusible inkjet media, however, in which polymeric particles react with an emulsifier compound.
Commonly assigned U.S. Ser. No. 10/881,127 discloses an inkjet recording element comprising a support having thereon in order from the top:
(a) a fusible, porous pigment-trapping layer comprising (i) fusible polymer particles comprising a thermoplastic polymer with reactive functional groups, (ii) a polyfunctional compound having complementary reactive functional groups capable of crosslinking the reactive functional groups on the thermoplastic polymer, and (iii) an optional binder; and
(b) an optional ink-carrier-liquid receptive layer. The support may also function as a liquid-absorbing sump layer either alone or in combination with the optional ink-carrier-liquid receptive layer.
Similarly, commonly assigned U.S. Ser. No. 10/881,264 discloses an inkjet recording element comprising a support having thereon, in order from the top:
(a) a fusible, porous ink-transporting layer comprising (i) fusible polymer particles comprising a thermoplastic polymer with reactive functional groups, (ii) a polyfunctional compound having complementary reactive functional groups capable of crosslinking the reactive functional groups on the thermoplastic polymer, and (iii) an optional binder;
(b) a fusible dye-trapping layer comprising fusible polymer particles, a dye mordant, and an optional hydrophilic binder; and
(c) an optional an ink-carrier-liquid receptive layer.
It is an object of this invention to provide an improved inkjet recording element comprising an upper porous layer that can be fused after printing, thereby obtaining high-density images. It is another object of the invention to provide an improved inkjet recording element having a protective upper porous layer that can be fused after printing to render images resistant to water and stain.